Leafcutter ants use bioweapons against enemies!

One of the major enemies of Atta colonies are Nomamyrmex army ants, highly-specialized, robust army ants who prey on young leaf-cutter colonies. The main deterrent against these army ants are of course the awesome soldiers of the leafcutters, but there are some interesting observations made that point to some other ways that leafcutter ants use so-called "bioweapons" to deter predation.

According to Ripley et al (Riley, et al. Journal of Natural History. The association of Amphisbaena alba - Reptilia: Amphisbaenia - with the leaf-cutting ant Atta cephalotes in Trinidad) there is a reptile (lizard) that is an inquiline in the nests of Atta cephalotes. Coincidentally, this lizard is known to prey on Nomamyrmex army ants. It also preys on other insects associated with the leafcutters, but only very rarely on the host workers ants themselves! Perhaps the loss of a few workers is good payment for harboring a bioweapon against one of their enemies?

"A. alba is a facultative inquiline in the nests of A. cephalotes. It has been excavated directly from nests. It can follow A. cephalotes's trail pheromone. Analysis of gut content & faecal material shows the reptile feeds primarily on insects associated with A. cephalotes & only occasionally on A. cephalotes. Other locations & Nomamyrmex are prey from museum specimens."

Thus, it seems that this reptile is inadvertantly or indirectly acting to protect the host colony!

The Mexican short-tailed snake (Sympholis lippiens), a secretive small snake that is occasionally found in tropical deciduous forest near Alamos in southern Sonora, has similar habits and is found in some nests of Atta mexicana. This species has oily, water-repellent skin, which is thought to provide some protection against the leafcutter ants. In the 1970's, Merv Larson, then the Director of the Arizona-Sonora Desert Museum, found one on a large organic debris mound of the Mexican leafcutter ant. Later, Howard Lawler and Gene Hall identified the stomach contents of a road-killed specimen, revealing that they eat beetle larvae. They theorized that the snake enters leafcutter nests in search of the larvae of beetle commensals that also live in leafcutter ant nests.

Another more interesting and spectacular observation has to do with nasute termites, whose formidable soldiers emit a stream of chemicals that entangle and kill attacking ants. According to one website, some Atta soldiers hold nasute soldiers in their mandibles and direct their emissions against invading Nomamyrmex ants! You might say that the leafcutter ants have evolved a way to use the nasute termites as "living guns"!

The website attributes these observations to Dr. James Wetterer and Monica Swarz, from 1987, but when I attempted to confirm this finding, I could not reach Dr. Schwarz and Dr. Wetterer said that this was "somewhat hard to believe" (which I took to mean he has never seen such a thing).

Nevertheless, it may be that the original basis for such an observation was the actual finding of nasute termites living in close proximity to Atta nests, whereupon the termites indirectly provided additional protection to the ants because of their nearby location.